Concentric shafts for remote independent variable vane actuation

ABSTRACT

An actuator system including a harmonic drive operable to drive a variable vane system of a gas turbine engine.

BACKGROUND

The present disclosure relates to a gas turbine engine and, moreparticularly, to a variable vane system therefor.

Gas turbine engines, such as those that power modern commercial andmilitary aircraft, generally include a compressor section to pressurizean airflow, a combustor section to burn a hydrocarbon fuel in thepresence of the pressurized air, and a turbine section to extract energyfrom the resultant combustion gases.

Some gas turbine engines include variable vanes that can be pivotedabout their individual axes to change an operational performancecharacteristic. Typically, the variable vanes are robustly designed tohandle the stress loads that are applied to change the position of thevanes. A mechanical linkage is typically utilized to rotate the variablevanes. Because forces on the variable vanes can be relativelysignificant, forces transmitted through the mechanical linkage can alsobe relatively significant. Legacy compressor designs typically utilizefueldraulic actuation to rotate the variable vanes.

SUMMARY

A gas turbine engine according to another disclosed non-limitingembodiment of the present disclosure can include a first actuator; afirst harmonic drive driven by the first actuator; a first drive shaftdriven by the first harmonic drive; a second actuator; a second harmonicdrive driven by the second actuator; and a second drive shaft driven bythe second harmonic drive, the first drive shaft coaxial with the seconddrive shaft.

A further embodiment of the present disclosure may include, wherein thefirst drive shaft and the second drive shaft extend through a firewall.

A further embodiment of the present disclosure may include, wherein thefirst drive shaft is operable to drive a first variable vane stage.

A further embodiment of the present disclosure may include, wherein thesecond drive shaft is operable to drive a second variable vane stage.

A further embodiment of the present disclosure may include, wherein theharmonic drive includes a strain wave gearing mechanism.

A further embodiment of the present disclosure may include, wherein thestrain wave gearing mechanism include a fixed circular spline, a flexspline attached to an output shaft, and a wave generator attached to aninput shaft, the flex spline driven by the wave generator with respectto the circular spline.

A further embodiment of the present disclosure may include, wherein theharmonic drive provides between a 30:1-320:1 gear ratio.

A further embodiment of the present disclosure may include, wherein theactuator is an electric motor.

A further embodiment of the present disclosure may include, wherein thefirst drive shaft and the second drive shaft are operable to drive arespective first unison ring and a second unison ring.

A further embodiment of the present disclosure may include, wherein thefirst drive shaft and the second drive shaft include a respective firstdrive gear and a second drive gear operable to drive a respective firstunison ring and a second unison ring.

A further embodiment of the present disclosure may include, wherein thefirst unison ring and the second unison ring include a respective gearsegment meshed with the respective first drive gear and the second drivegear.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be appreciated; however, the following descriptionand drawings are intended to be exemplary in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art fromthe following detailed description of the disclosed non-limitingembodiment. The drawings that accompany the detailed description can bebriefly described as follows:

FIG. 1 is a schematic cross-section of an example gas turbine enginearchitecture;

FIG. 2 is a perspective view of a variable vane system for a gas turbineengine;

FIG. 3 is a partial perspective view of one stage of a variable vanesystem for a gas turbine engine;

FIG. 4 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 5 is a perspective view of a variable vane system for a gas turbineengine;

FIG. 6 is a schematic view of harmonic drive system;

FIG. 7 is an expanded perspective view of a variable vane system for agas turbine engine according to one disclosed non-limiting embodiment;

FIG. 8 is a side view of the variable vane system of FIG. 7;

FIG. 9 is a side view of a variable vane system for a gas turbine engineaccording to one disclosed non-limiting embodiment;

FIG. 10 is an expanded perspective view of the variable vane system ofFIG. 9;

FIG. 11A is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 11B is an expanded sectional view of the unison ring of FIG. 11A;

FIG. 12 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 13 is a expanded partial sectional view of a variable vane systemfor a gas turbine engine according to one disclosed non-limitingembodiment;

FIG. 14 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 15 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 16 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 17 is a schematic view of the variable vane system of FIG. 16 in afirst position;

FIG. 18 is a schematic view of the variable vane system of FIG. 16 in asecond position;

FIG. 19 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 20 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 21 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 22 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 23 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 24 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 25 is a plan view of a link for use in the system of FIG. 24;

FIG. 26 is a schematic view of the variable vane system of FIG. 24 in afirst position;

FIG. 27 is a schematic view of the variable vane system of FIG. 24 in asecond position;

FIG. 28 is a sectional view of the link of FIG. 25;

FIG. 29 is a sectional view of a unison ring for a variable vane systemfor a gas turbine engine according to one disclosed non-limitingembodiment;

FIG. 30 is a schematic view of a variable vane system for a gas turbineengine according to one disclosed non-limiting embodiment;

FIG. 31 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 32 is a sectional view of the variable vane system of FIG. 31;

FIG. 33 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 34 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 35 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 36 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 37 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

FIG. 38 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment; and

FIG. 39 is a perspective view of a variable vane system for a gasturbine engine according to one disclosed non-limiting embodiment;

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool GTF (gearedturbofan) that generally incorporates a fan section 22, a compressorsection 24, a combustor section 26 and a turbine section 28. Alternativeengine architectures might include an augmentor section and exhaust ductsection (not shown) among other systems or features. The fan section 22drives air along a bypass flowpath while the compressor section 24drives air along a core flowpath for compression and communication intothe combustor section 26 then expansion thru the turbine section 28.Although depicted as a GTF in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with GTF as the teachings may be applied to other types ofturbine engines such as a Direct-Drive-Turbofan with high, or low bypassaugmented turbofan, turbojets, turboshafts, and three-spool (plus fan)turbofans wherein an intermediate spool includes an intermediatepressure compressor (“IPC”) between a Low Pressure Compressor (“LPC”)and a High Pressure Compressor (“HPC”), and an intermediate pressureturbine (“IPT”) between the high pressure turbine (“HPT”) and the Lowpressure Turbine (“LPT”).

The engine 20 generally includes a low spool 30 and a high spool 32mounted for rotation about an engine central longitudinal axis Arelative to an engine static structure 36 via several bearingcompartments 38. The low spool 30 generally includes an inner shaft 40that interconnects a fan 42, a low pressure compressor 44 (“LPC”) and alow pressure turbine 46 (“LPT”). The inner shaft 40 drives the fan 42directly or thru a geared architecture 48 to drive the fan 42 at a lowerspeed than the low spool 30. An exemplary reduction transmission is anepicyclic transmission, namely a planetary or star gear system.

The high spool 32 includes an outer shaft 50 that interconnects a highpressure compressor 52 (“HPC”) and high pressure turbine 54 (“HPT”). Acombustor 56 is arranged between the HPC 52 and the HPT 54. The innershaft 40 and the outer shaft 50 are concentric and rotate about theengine central longitudinal axis A which is collinear with theirlongitudinal axes.

Core airflow is compressed by the LPC 44 then the HPC 52, mixed withfuel and burned in the combustor 56, then expanded over the HPT 54 andthe LPT 46. The turbines 54, 46 rotationally drive the respective lowspool 30 and high spool 32 in response to the expansion. The main engineshafts 40, 50 are supported at a plurality of points by the bearingcompartments 38. It should be understood that various bearingcompartments 38 at various locations may alternatively or additionallybe provided.

In one example, the gas turbine engine 20 is a high-bypass gearedaircraft engine with a bypass ratio greater than about six (6:1). Thegeared architecture 48 can include an epicyclic gear train, such as aplanetary gear system or other gear system. The example epicyclic geartrain has a gear reduction ratio of greater than about 2.3:1, and inanother example is greater than about 3.0:1. The geared turbofan enablesoperation of the low spool 30 at higher speeds which can increase theoperational efficiency of the LPC 44 and LPT 46 to render increasedpressure in a relatively few number of stages.

A pressure ratio associated with the LPT 46 is pressure measured priorto the inlet of the LPT 46 as related to the pressure at the outlet ofthe LPT 46 prior to an exhaust nozzle of the gas turbine engine 20. Inone non-limiting embodiment, the bypass ratio of the gas turbine engine20 is greater than about ten (10:1), the fan diameter is significantlylarger than that of the LPC 44, and the LPT 46 has a pressure ratio thatis greater than about five (5:1). It should be understood, however, thatthe above parameters are only exemplary of one embodiment of a gearedarchitecture engine and that the present disclosure is applicable toother gas turbine engines including direct drive turbofans, where therotational speed of the fan 42 is the same (1:1) of the LPC 44.

In one example, a significant amount of thrust is provided by the bypassflow path due to the high bypass ratio. The fan section 22 of the gasturbine engine 20 is designed for a particular flightcondition—typically cruise at about 0.8 Mach and about 35,000 feet(10668 meters). This flight condition, with the gas turbine engine 20 atits best fuel consumption, is also known as bucket cruise ThrustSpecific Fuel Consumption (TSFC). TSFC is an industry standard parameterof fuel consumption per unit of thrust.

Fan Pressure Ratio is the pressure ratio across a blade of the fansection 22 without the use of a Fan Exit Guide Vane system. Therelatively low Fan Pressure Ratio according to one example gas turbineengine 20 is less than 1.45. Low Corrected Fan Tip Speed is the actualfan tip speed divided by an industry standard temperature correction of(“T”/518.7)^(0.5) in which “T” represents the ambient temperature indegrees Rankine. The Low Corrected Fan Tip Speed according to oneexample gas turbine engine 20 is less than about 1150 fps (351 m/s).

With reference to FIG. 2, one or more stages of the LPC 44 and/or theHPC 52 include a variable vane system 100 that can be rotated to changean operational performance characteristic of the gas turbine engine 20for different operating conditions. The variable vane system 100 mayinclude one or more variable vane stages.

The variable vane system 100 may include a plurality of variable vanes102 circumferentially arranged around the engine central axis A. Thevariable vanes 102 each include a variable vane body that has an airfoilportion that provides a lift force via Bernoulli's principle such thatone side of the airfoil portion generally operates as a suction side andthe opposing side of the airfoil portion generally operates as apressure side. Each of the variable vanes 102 generally spans between aninner diameter and an outer diameter relative to the engine central axisA.

With reference to FIG. 3, each of the variable vanes 102 includes aninner pivot pin 104 that is receivable into a corresponding socket (notshown) and an outer trunion 106 mounted through an outer case 108 suchthat each of the variable vanes 102 can pivot about a vane axis V. Theouter trunion 106 is defined along the vane axis V (FIG. 3).

With reference to FIG. 4, the variable vane system 100 further includesa unison ring 110 to which, in one disclosed non-limiting embodiment,each of the outer trunions 106 are attached through a drive arm 112along a respective axis D. It should be appreciated that although aparticular drive arm 112 is disclosed in this embodiment, variouslinkages of various geometries may be utilized.

The variable vane system 100 is driven by an actuator system 118 with anactuator 120, a harmonic drive 122 and an actuator arm 124. Althoughparticular components are separately described, it should be appreciatedthat alternative or additional components may be provided. Although asingle actuator system 118 may be utilized for each stage (FIG. 5),multiple actuator systems 118 may be provided on a single stage (FIG. 5)to facilitate additional stability for each singe unison ring 110.

The actuator 120 may include an electric motor or other electric powereddevice. The actuator 120 is defined along an axis B.

The harmonic drive 122 includes a strain wave gearing mechanism 130that, in one example, may provide a 30:1-320:1 gear ratio in a compactpackage that significantly reduces the rotation and increases the torqueprovided by the actuator 120. The strain wave gearing mechanism 130generally includes a fixed circular spline 132, a flex spline 134attached to an output shaft 136 along an axis B, and a wave generator138 attached to an input shaft 140 which is connected to the actuator120 along axis B (FIG. 6).

The harmonic drive 122 essentially provides no backlash, compactness andlight weight, high gear ratios, reconfigurable ratios within a standardhousing, good resolution and excellent repeatability when repositioninginertial loads, high torque capability, and coaxial input and outputshafts. The harmonic drive 122 thereby prevents back driving by therelatively high aerodynamic forces experienced by the variable vanes102.

The harmonic drive 122 need only rotate the drive arm 124 through about90 degrees and, in a more specific embodiment, only about 0-40 degreesto drive rotation of the unison ring 110, thence the individual variablevanes 102 through the respective drive arms 112. That is, the actuatorarm 124 rotates the unison ring 110 that, in turn, rotates the drivearms 112 along their respective axis D to rotate the trunions 106, andthus the variable vanes 102 about axis V.

With reference to FIG. 7, in another disclosed embodiment, the actuatorsystem 118A includes a geared connection 140 between the harmonic drive122 and a drive gear 142 that is meshed with an actuator gear 144mounted to a trunion 106 of a variable vane 102. The actuator gear 144may be a gear segment of about ninety degrees.

The other variable vanes 102 are attached to the unison ring 110 thoughrespective links 146. The geared connection 140 provides for an offsetto accommodate insufficient space for a direct connection attachedconcentric to the axis of a variable vane, such as the first LPCvariable vane stage that is typically adjacent to a structural wall 148such as a firewall (FIG. 8).

With reference to FIG. 9, in another disclosed embodiment, the actuatorsystem 118C includes an axial geared connection 150 such that theactuator system 118C is generally axial with the engine axis A forinstallations with limited vertical packaging space. In this embodiment,the geared connection 150 includes a drive gear 152 that is meshed withan actuator gear 154 mounted to a trunion 106 in a generallyperpendicular arrangement (FIG. 10). Alternatively, the gearedconnection 150 can be angled relative to the vane actuator via a bevelgear.

With reference to FIG. 11A, in another disclosed embodiment, theactuator system 118D includes an extended geared unison ring 160 thatspans at least a first variable vane stage 162 with a vane gear 164 foreach first stage variable vane trunion 106 and a second variable vanestage 166 with a vane gear 168 for each second stage variable vanetrunion 106. The extended geared unison ring 160 includes an associatedfirst gear rack 170 and a second gear rack 172 that interface with therespective vane gears 164, 168. This minimizes or eliminates axialmotion of the extended geared unison ring 160. In this embodiment, thegeared connection 180 includes a drive gear 182 that is meshed with anactuator gear 184 on the extended geared unison ring 160. The actuatorgear 184 need be only a relatively short gear rack segment.

With reference to FIG. 11B, the extended geared unison ring 160 includesan interface 174 with the outer case 108. The outer case 108 may includea flange 176 to restrain axial movement of the extended geared unisonring 160. Low friction devices 178 such as bumpers of low frictionmaterial, rollers, or other devices may be alternatively, oradditionally, provided.

With reference to FIG. 12, in another disclosed embodiment, the actuatorsystem 118D may utilize a geared unison ring 190 to drive a firstvariable vane stage 192 with a vane gear 194 mounted to each first stagevariable vane trunion 106. A flange 176, or flange segments, may axiallyrestrain the geared unison ring 160 on the outer case 108 to stabilizethe geared unison ring 160 and avoid hysteresis (FIG. 13).

With reference to FIG. 14, in another disclosed embodiment, the actuatorsystem 118E may utilize a multi-planar gear 200. The multi-planar gear200 includes a first set of gear teeth 202 in a first plane 204 and asecond set of gear teeth 206 in a second plane 208.

The first plane 204 and the second plane 208 are offset such that thefirst set of gear teeth 202 are in mesh with a first drive gear 210 fora drive variable vane 102 in a first stage 212 and the second set ofgear teeth 206 in mesh with a second drive gear 214 for a drive variablevane 102 in a second stage 216. The first drive gear 210 and the seconddrive gear 214 may be arranged at different heights to interface withthe multi-planar gear 200. Since actuation requires only partialrotation, symmetry of the multi-planar gear 200 is not necessary. Thegear ratio can be adjusted to provide different vane rotations perstage.

The first drive gear 210 and the second drive gear 214 also include adrive arm 218, 220 to rotate a respective unison ring 222, 224. Thedriven variable vanes 102 are connected their respective unison ring222, 224 by a respective linkage 226,228 for each variable vane 102.

With reference to FIG. 15, in another disclosed embodiment, the actuatorsystem 118E may include a multiple of idler gears 230, 231 thatinterconnect drive gears 232, 234, 236 of each of a multiple of stages238, 240, 242. Each of the multiple of idler gears 230 may be mounted tostatic structure (not shown) through a shaft 240, 242 such that themultiple of idler gears 230 may be positioned above the variable vanestructure. Alternatively, the idler gears 230 may be mounted directly toa variable vane to direct drive a driving vane.

In this embodiment, a multi-planar gear 232 may be driven by a driveshaft 240 driven by a remote actuator.

With reference to FIG. 16, in another disclosed embodiment, the actuatorsystem 118F may utilize a geared unison ring 260. The geared unison ring260 locates a gear 262 on an outer diameter of the geared unison ring260.

Rotation of the geared unison ring 260 by the actuator system 118Fdrives the individual variable vanes 102 through the respective drivearms 204. The actuator system 118F is generally axial with the engineaxis A for installations with limited vertical packaging space. Theactuator system 118F drives a drive gear 264 that is wider than the gear262 as the rotation of the unison ring 260 results in a relatively smallamount of axial motion (FIGS. 17 and 18). This will require a smallamount of sliding between gear teeth of the gears 262, 264, but therotation required to actuate the variable vanes is relatively small,typically, only a few degrees, and the actuation is slow, so a smallamount of sliding may be acceptable.

With reference to FIG. 19, in another disclosed embodiment, the drivegear 264 may be an extended shaft with a multiple of gear segments 268,270 to drive a respective multiple of unison rings 272, 274.

With reference to FIG. 20, in another disclosed embodiment, the actuatorsystem 118G may utilize a cable drive system 280. The cable drive system280 includes a drum 282, or alternatively, a drum segment 282A (FIG. 21)with a groove 284 within which a cable 286 is at least partiallyreceived.

The groove 284 defines a contoured path to guide the cable 286 (FIG. 22,23). The cable 286 defines a path that is contoured to avoid slack inthe cable 286. Alternatively, a tension-loading device may be used. Thecable 286 is connected to the unison ring 288 such that cable 286 willalways remain tangential to the unison ring 288.

With reference to FIG. 24, in another disclosed embodiment, the actuatorsystem 118H may utilize a multiple of drive arms 300 which actuate theindividual variable vanes 102. Each of the multiple of drive arms 300includes a slot 302 that permits single point actuation (FIG. 25). Eachslot 302 for each drive arm 300 receives a respective pin 304 thatextends from the unison ring 306. The axial motion is absorbed (FIGS. 26and 27) in the slots 302 of the individual links, so that the unisonring 306 is effectively stabilized, even with single point actuation.Each respective pin 304 that extends from the unison ring 306 and/orslot 302 may be tapered to permit rotation of the unison ring 306 withminimal play (FIG. 28).

With reference to FIG. 29, the unison ring 306 has a “U” shaped crosssection that provides significant stiffness while being light in weight.The unison ring 306 is supported on the engine case by a multiple ofsupports 308 that are arranged around the engine case. The support 308may be generally cross-shaped to support a multiple of rollers 310. Inthis example, each roller 310 interacts with an upper surface 312, aforward surface 314, and an aft surface 316 of the unison ring 306.

With reference to FIG. 30, a single drive shaft 320 may include multipledrive gears 322, 324, 326 meshed with respective gear racks 328, 330,332 of the associated unison rings 334, 336, 338 of each variable vanestage. The gear racks 328, 330, 332 are axially offset on the unisonring 334, 336, 338 to provide an extremely low profile.

With reference to FIG. 31, in another disclosed embodiment, the actuator120 and the harmonic drive 122 are remotely located on one side of afirewall 350 with a drive shaft 352 from the harmonic drive 122 thatextends therethrough to drive a HPC variable vane system 360 which is ina higher temperate environment. The extended drive shaft 352 permits theactuator 120 and the harmonic drive 122 to be located in a desirableenvironment. The extended drive shaft 352 may mesh with the single driveshaft 320 to drive a multiple of variable vane stages (FIG. 32).

With reference to FIG. 33, in another disclosed embodiment, an actuatorsystem 1181 includes a drive shaft 360 operable to control multiplestages of variable vanes (four shown).

With reference to FIG. 34, in another disclosed embodiment, if an axis Vof the variable vane is aligned planer with the drive shaft 360, a vanedrive bevel gear 370 may drive a unison ring 372, and thus all thevariable vanes 374 (FIGS. 26 and 27) in a direct manner.

Alternatively, an additional actuation arm 380 may extend from the vanedrive bevel gear 382 to provide the same linkage motion to the unisonring 384 as the actuation arms on the variable vanes, but is aligned tothe bevel gear 382. The unison ring 384 may include a bridge 386 whichbridges a subset of a multiple of variable vane drive arms 388. That is,the bridge 386 is mounted to the unison ring 384 to which the multipleof variable vane drive arms 388 are attached. The actuation arm 380,since not tied directly to a variable vane, is mounted to staticstructure 390.

With reference to FIG. 35, in another disclosed embodiment, a driveshaft 400 and gears 402 may be enclosed in a gear box 404 that ismounted to an engine case 406. The drive shaft 400 has a single input408 and a multiple of outputs 410, 412, 414, 416.

The gearbox 404 may house all the necessary supports and bearings andmay be mounted directly to the engine case 406 such as a HPC case. Thegearbox 404 also provides a static structure from which to rotationallymount the variable vane actuation arms 420, 422 that are not tieddirectly to a variable vane 418, 424. The variable vane actuation arms420, 422 may be mounted to a bridge 424, 426 that is mounted to therespective unison ring 428, 430.

With reference to FIG. 36, in another disclosed embodiment, a driveshaft 440 drives a multiple of links 442 (four shown) which drive abridge 450-456 to respective unison ring. Although the links 442-448 areshown as linear, the links may alternatively be curved to conform thecurvature of the case to provide a more compact package. Alternativelystill, if there is sufficient space between stages, the bridge 450-456may be mounted to a side of the respective unison ring to provide a morecompact mechanism.

With reference to FIG. 37, in another disclosed embodiment, a driveshaft 460 drives a multiple of links 462 (four shown) which drive abridge 464 to respective unison ring 466. The links 462 are driven toprovide a linear relationship between the vane rotation angles acrossall the stages. That is, as the first stage vane angle changes, each ofthe other stages will change based on a fixed ratio off the first.Alternatively, a non-linear relationship may be provided for optimalperformance. The non-linear relationship may be optimized as, for eachstage, there are 5 variables available: 2 initial angles (D, E) andthree lengths (F, G, H). These variables may be specifically tailored toprovide a resultant output from the drive shaft 460 that differs foreach stage (four shown).

With reference to FIG. 38, in another disclosed embodiment, an actuatorsystem 118J may include a first actuator 480, a first harmonic drive482, a first drive shaft 484, a second actuator 486, a second harmonicdrive 488, and a second drive shaft 490. The actuators 480, 486 and theharmonic drives 482, 488 may be located on a side of firewall 500, thatprovides a thermally controlled environment. In one example, thethermally controlled environment is about 160F. The first drive shaft484 and the second drive shaft 490 are coaxial and pass through thefirewall 500 into a higher temperature environment of, for example,200F-600F.

With reference to FIG. 39, the first drive shaft 484 and the seconddrive shaft 490 are independently actuated to respectively control avariable vane stage 502, 504. The first drive shaft 484 and the seconddrive shaft 490 are operable to drive respective gears 506, 508 in asiding gear arrange as described above to drive respective unison rings510, 512 (FIGS. 17, 18). The respective distal end 520, 522 of the firstdrive shaft 484 and the second drive shaft 490 may be supported by asupport bracket 530 mounted to the engine case.

The actuator system 118J permits variable vane stages to be actuatedindependently from a remote distance to provide thermal isolation behinda firewall, or because the motors must be relocated due to limitedpackaging space.

Although the different non-limiting embodiments have specificillustrated components, the embodiments of this invention are notlimited to those particular combinations. It is possible to use some ofthe components or features from any of the non-limiting embodiments incombination with features or components from any of the othernon-limiting embodiments.

It should be understood that relative positional terms such as“forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like arewith reference to the normal operational attitude of the vehicle andshould not be considered otherwise limiting.

It should be understood that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein, however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reasonthe appended claims should be studied to determine true scope andcontent.

What is claimed is:
 1. A gas turbine engine, comprising: a firstactuator; a first harmonic drive driven by the first actuator; a firstdrive shaft driven by the first harmonic drive; a second actuator; asecond harmonic drive driven by the second actuator; and a second driveshaft driven by the second harmonic drive, the first drive shaft coaxialwith the second drive shaft.
 2. The gas turbine engine as recited inclaim 1, wherein the first drive shaft and the second drive shaft extendthrough a firewall.
 3. The gas turbine engine as recited in claim 1,wherein the first drive shaft is operable to drive a first variable vanestage.
 4. The gas turbine engine as recited in claim 3, wherein thesecond drive shaft is operable to drive a second variable vane stage. 5.The gas turbine engine as recited in claim 1, wherein the harmonic driveincludes a strain wave gearing mechanism.
 6. The gas turbine engine asrecited as recited in claim 5, wherein the strain wave gearing mechanisminclude a fixed circular spline, a flex spline attached to an outputshaft, and a wave generator attached to an input shaft, the flex splinedriven by the wave generator with respect to the circular spline.
 7. Thegas turbine engine as recited in claim 1, wherein the harmonic driveprovides between a 30:1-320:1 gear ratio.
 8. The gas turbine engine asrecited in claim 1, wherein the actuator is an electric motor.
 9. Thegas turbine engine as recited in claim 1, wherein the first drive shaftand the second drive shaft are operable to drive a respective firstunison ring and a second unison ring.
 10. The gas turbine engine asrecited in claim 1, wherein the first drive shaft and the second driveshaft include a respective first drive gear and a second drive gearoperable to drive a respective first unison ring and a second unisonring.
 11. The gas turbine engine as recited in claim 10, wherein thefirst unison ring and the second unison ring include a respective gearsegment meshed with the respective first drive gear and the second drivegear.